The present invention generally relates to cooling systems for electrical equipment. More particularly, the present invention relates to cooling electrical protective devices such as fuses that are attached to electrical terminals. Electrical power converter units are vital and expensive components used in a variety of electric power system applications such as metal rolling mills and transportation systems. Power converters must be cooled to maintain their proper operating temperature. In a typical air-cooled power converter unit, heat generated by the unit is removed by free or forced convection to the ambient air to maintain the unit""s operating temperature within an acceptable range. Although some units are air-cooled, higher power units often generate too much heat to be sufficiently cooled by free or forced convection of heat to the ambient air. Consequently, such high power units may be liquid-cooled. Power converter units typically utilize auxiliary devices. In air-cooled units, such devices are usually sufficiently cooled by free convention (also referred to as passive cooling) or forced convection (also referred to as active cooling) of heat to the ambient air. However, auxiliary devices on liquid-cooled units, may not be sufficiently cooled by the air. One type of auxiliary device that may require additional cooling when attached to a liquid-cooled unit, or even a high-powered air cooled unit, is the electrical fuses or fuse arrays. The purpose of fuses is to isolate the power converter circuits or other electrical components and equipment during an electrical fault event by melting their elements, severing the electrical circuit, and stopping the flow of electric current. This isolation limits the damage from high electrical currents during a fault. Since the fuses produce waste heat in normal operation, they must be cooled to maintain temperature limits for proper power converter protection and fuse life. When a higher-powered unit is designed, additional fuses may be added to an existing fuse array to help increase the power rating, but the fuses may no longer be electrically coordinated with the power converter. The fusesxe2x80x9d elements must be coordinated, with respect to thermal capacity and arc voltage, with the power converter components they are protecting. Thermal capacity electrical coordination is the coordination of thermal capacity of the fuses with the power converter electrical conductors (which may be calculated by electrical current squared and multiplied by time, or I2t). Electrical arc voltage coordination is the coordination of the voltage level created when the fuse elements melt with the voltage level that can be withstood by the electrical components, equipment and insulation system. Simply adding more fuses to a fuse limited unit may not provide the required electrical coordination, and may increase the cost of the fuse array. Thus it is desirable, from both a performance standpoint and an economic standpoint, to use an existing fuse array or a slightly modified fuse array on liquid-cooled units and on air-cooled units that are fuse limited and may be converted to higher powered units. A solution that may allow the use of existing fuse arrays on a higher-powered unit is to use actively cooled fuses. Some fuses can operate at higher power levels when they are actively cooled. A power converter being designed as a high powered unit or an air cooled unit that is being refitted as a higher-powered unit may require few or no additional fuses to handle the increased power load if the fuses are actively cooled. One method of actively cooling the fuses is to force air over them. Although forced-air cooling may provide a cooling benefit, such systems may cause additional problems. For example, the increased volume of air flowing to the fuses carries with it an increased amount of particulate matter and other contaminants, which may condense on and around the fuses and other power converter devices and cause malfunctions. In addition, cooling the fuses with forced air may provide inconsistent cooling of the individual fuses in the array. For example, there is usually a narrow gap between the ends of the fuses and the electrical connection terminal and a narrow gap between fuse bodies. Such narrow gaps may restrict the airflow, causing insufficient cooling. Local heat build-up at the fuse ends could substantially degrade the performance and life of the fuses. In order for the electrically parallel fuses in an array to evenly share an electrical current, the individual fuses must be maintained at the same temperature. Due to these and other problems, it would be desirable to provide an improved apparatus for cooling fuse arrays that can be added to existing power converters or incorporated into new power converter designs to allow existing or slightly modified fuse arrays to operate at an increased power rating. It also would be desirable to provide such an apparatus at a minimal cost. In addition, because power converter units are typically used in industrial and commercial applications, making down time for repairs or refitting expensive, it also would be desirable to provide an improved apparatus that can be installed quickly and easily to minimize down time.
The present invention overcomes the problems discussed above, and provides additional advantages, by employing a fluid cooling apparatus that cools electrical protective devices, such as fuse arrays having one or more fuses, mounted to electrical terminals.
Exemplary embodiments of the invention have one or more coolant passages attached to a pair of electrical terminals in a thermally conductive manner. Several coolant conduits are connected to the coolant passages and connected to a pressurized coolant source. The pressurized coolant source passes a cooling fluid through the conduits and passages, thereby directly cooling the terminals and indirectly cooling the fuse array. An exemplary embodiment may employ heat exchangers to cool the cooling fluid between successive passes to the electrical terminals. The cooling apparatus may also be used in conjunction with ambient air cooling of the fuses or other cooling systems.
In another exemplary embodiment of the apparatus of the present invention, the apparatus has a pair of coolant passages, each bent to have two roughly parallel portions. Each bent coolant passage is, for example, attached to one of the terminals by brazing the parallel portions to the terminal such that they divide each connection terminal into three approximately equally sized regions. The two terminals are interconnected by six fuses, which are attached to the terminals at each end of the fuses. Two fuses are located in each of the connection terminal regions noted above. Several coolant conduits are connected to the bent coolant passages and are connected to a pressurized coolant source, which passes cooling fluid through the conduits and the passages.
In an exemplary embodiment of the invention the electrical current rating of the fuses may be increased above their normal electrical current rating. In another exemplary embodiment, the service life of the fuses may be increased above their normal life. In yet another exemplary embodiment of the invention, the electrical current rating and service life of the fuses are increased while maintaining thermal capacity coordination (which may be calculated by I2t) or electrical arc voltage coordination between the fuses and a power converter protected by the fuses.
In another exemplary embodiment of the invention, waste heat generated by the fuses is removed, thereby reducing the ambient air temperature and increasing air cooling to other devices being operated in conjunction with the fuses. In yet another exemplary embodiment, the waste heat removed from the fuses is employed to provide benefits to other parts of a system.